change(state): Make the types for finalized blocks consistent

[upbqdn]

Motivation

Close #7273. I initially wanted to summarize the discussion that the issue points to in the issue description, but I ended up fixing the code itself because I thought it was easier.

The issue was that we were using SemanticallyVerifiedBlock and SemanticallyVerifiedBlockWithTrees for blocks that the finalized state commits to its database. Doing so is not what we want because, as Teor said:

Also, I don't think we should be downgrading verification status from contextual or checkpoint to semantic, unless it's a quick downgrade using into(), and then calling a common verification function. Most of the time we've already done that verification on those types though!

PR Author Checklist

• Will the PR name make sense to users?
• Does the PR have a priority label?
• Have you added or updated tests?
• Is the documentation up to date?

Solution

• Use a new structure called FinalizedBlock instead of SemanticallyVerifiedBlockWithTrees, and also use it when writing a finalized block into the database.
• This PR doesn't really change any logic in the state. It is only a structural refactor.

Reviewer Checklist

Check before approving the PR:

• Does the PR scope match the ticket?
• Are there enough tests to make sure it works? Do the tests cover the PR motivation?
• Are all the PR blockers dealt with?
  PR blockers can be dealt with in new tickets or PRs.

And check the PR Author checklist is complete.

[teor2345]

Thanks for this, I have some optional suggestions about standard trait derives (and documenting them).

[teor2345]

I added the CI failure to ticket #7898 because it seemed very similar.